Array antennas have a function of beam convergence, and therefore are widely used in the communications field. For example, a phased-radar array antenna includes hundreds or even thousands of elements. For another example, for a multi-sector communications antenna of a base station, each sector implements beam width control in horizontal and pitching directions by means of antenna arraying to achieve signal coverage in a specific area and provide higher gains to obtain a farther communication distance. In addition, an array antenna can also be used to implement estimation of a direction of arrival and the like.
An array antenna is an apparatus with multiple antenna elements included in an antenna. According to requirements, an arrangement manner for elements in an array antenna may be one-dimensional line arrangement, two-dimensional plane arrangement, conformal arrangement on a specific target surface, or three-dimensional arrangement. The specific arrangement may be equally-spaced regular arrangement, or unequally-spaced arrangement may be used when required. Indicators for an array antenna mainly include a gain, a side lobe level (SLL), a beam width, system costs, and the like. Focuses on the indicators vary according to different application scenarios. In applications of the communications field, the system costs and the SLL are most common concerns. A lower SLL helps a system exert better interference resistance performance.
An SLL of an array antenna is mainly determined by an array arrangement manner, and feeding amplitudes and phases of array elements. For a linear array or a matrix array with equally-spaced regular arrangement, an SLL is approximately fixed at about 13.5 dB, specifically determined by factors such as radiation patterns of the elements, a spacing between the elements, and mutual coupling between the elements. In addition, the spacing between the elements is strictly limited within one wavelength to avoid grating lobes. Excited amplitude weighting for the array elements can decrease the SLL but reduce aperture efficiency as well. This does not decrease the system costs but increases difficulties in implementing a system design, thereby applicable to a relatively narrow scope.
In the field of millimeter band communications, especially the field of high-frequency millimeter band communications, for example, when a working wavelength of a 60 GHz millimeter band is only 5 mm, a size of an element in a corresponding array antenna is usually smaller than half a wavelength, that is 2.5 mm. In this case, a transmit-receive component of a system usually integrates receive and transmit antenna arrays. However, for a system working in a frequency division duplexing (FDD) mode, since a radio frequency device such as a duplexer is difficult to be integrated, a transmit-receive antenna array is usually integrated in a form in which a receive antenna array and a transmit antenna array are separated from each other. In appearance, this is manifested by a separate receive antenna array (RX array for short) and a separate transmit antenna array (TX array for short), and the TX array and the RX array together form a TR antenna array. FIG. 1 is a schematic diagram of a TR antenna array, where a TX array or an RX array may be arranged as an array antenna in any form. The array antenna is generally arrayed by using the TR antenna array shown in FIG. 1, which is also known as secondary arraying.
To meet requirements for long distance communications, multiple TR antenna arrays may be required for secondary arraying. Refer to FIG. 2, which is a schematic diagram of multiple TR antenna arrays arranged as an array antenna. A direction along which one TX array and another TX array are not continuous and one RX array and another RX array are not continuous is referred to as a discontinuous arraying direction, and a direction along which multiple TX arrays are continuous and multiple RX arrays are continuous is referred to as a continuous arraying direction. However, since a TX array and an RX array usually have a size greater than one working wavelength and are physically separated from each other, using the typical regular arrangement method of a TR antenna array may introduce a problem of grating lobes or high side lobes. As a result, a system does not have a strong interference resistance capability or even cannot work normally.